Superconducting properties and rapid heating condition in transformed jelly-roll Nb₃Al multifilamentary wires as a function of maximum ohmic-heating temperature

Jelly-roll Nb₃Al wires with a Nb matrix were ohmically-heated to maximum temperatures ranging from 1800 to 2300°C in vacuum in order to optimize the ohmic-heating conditions and to investigate the superconducting properties for this transformation method. The diameters of these wires were 0.80-1.34 mm. Surface temperature at the central point of the sample was measured by a photodiode during rapid ohmic-heating. After the surface temperature reached a maximum, the sample was quenched in liquid gallium. All the samples were annealed at 800°C for 3-25 hours after the rapid heating process to transform the bcc-phase to the A15 phase. Critical currents were measured up to 23 T. The samples heated to 2000°C showed a maximum critical current density of 64 A/mm² at 20 T. The critical current density decreased with increasing maximum temperature during rapid heating. This paper describes the superconducting properties, the rapid heating conditions and the achievement of high critical current density at high magnetic fields.